The modification of epoxy resins in the preparation of cationic paint binders is extensively described in the literature. Such modifications include the introduction of protonable groups, as well as the extension of the polymer chain by reaction with polyfunctional compounds, such as difunctional compounds, or through the introduction of groups which serve to crosslink the applied paint films.
The molecular constituents heretofore used to prolong the chain are either simple difunctional compounds such as diphenols, diols or dicarboxylic acids, or the more complex intermediates which, in addition to their function as chain extenders, carry groups which influence the applied paint film, such as the longer hydrocarbon radicals, polyglycol radicals, urea, or amide groups. Crosslinkable groups such as polymerizable double bonds or blocked isocyanate groups can be introduced through reaction of corresponding monoisocyanate compounds with the hydroxy groups of the resin.